1. Field of the Invention
The present invention relates to digital image processing, and particularly relates to an image processing technology that performs blurring on an image.
2. Description of the Related Art
In recent years, there is proposed a compact digital camera capable of obtaining an excellent blur by increasing the size of an image sensor. However, when the size of the image sensor is increased, the size of an image-forming optical system is also increased so that it becomes difficult to reduce the size of the camera. To cope with this, Japanese Patent Application Laid-open No. 2000-207549 discloses a camera in which blurring is performed by picking up an image that is nearly in deep focus (a state where all areas are in focus), acquiring information on the distance to a subject, and performing predetermined image processing on the picked-up image.
However, even when the deep-focus image is to be picked up, in reality, it is not possible to obtain an image which is perfectly focused in all areas due to influences of diffraction caused by an aperture and image plane aberration, and a difference in object distance. Particularly in a compact digital camera, the influence of the diffraction or the aberration tends to be increased. To cope with this, Japanese Patent Application Laid-open No. 2011-211663 discloses an invention in which an image degraded by the influence of the diffraction or aberration is restored by digital processing.
In a case where blurring processing in which the focus position of a picked-up image is changed is performed, when the picked-up image is not a strictly deep-focus image, there arises a problem that the image quality after the blurring is degraded, i.e., apart that should be in focus is blurred. In addition, there is a problem that, even in the part in focus, the image is degraded by the influence of the diffraction or aberration and a blurred image having high image quality cannot be obtained.